HIP IMPACT VELOCITIES AND BODY CONFIGURATIONS FOR VOLUNTARY FALLS FROM STANDING HEIGHT

Fall dynamics have largely been ignored in the study of hip fracture e tiology and in the development of hip fracture prevention strategies. In this study, we asked the following questions: (1) What are the rang es of hip impact velocities associated with a sideways Fall from stand ing height? (2) What are the ranges of body configurations at impact? and (3) How do protective reflexes such as muscle activation or using an outstretched hand influence fall kinematics? To answer these questi ons, we recruited six young healthy athletes who performed voluntary s ideways falls on a thick foam mattress. Several categories of falls we re investigated: (a) muscle-active vs muscle-relaxed falls; (b) falls From a standing position or from walking; and (c) falls in which an ou tstretched arm was used to break the fall. Each fall was videotaped at 60 frames s(-1). Fall kinematics parameters were obtained by digitizi ng markers placed on anatomical points of interest. The mean value for vertical hip impact velocity was 2.75 ms(-1) (+/-0.42 ms(-1) [S.D.]). The mean value for trunk angle (the angle between the trunk and the v ertical) was 17.3 degrees (+/-11.5 degrees [S.D.]). We found a 38% red uction in the trunk angle at impact, and a 7% reduction in hip impact velocity for relaxed vs muscle-active falls. Finally, regarding the fa lls in which an outstretched arm was used, only two out of the six sub jects were able to break the Fall with their arm or hand. For the rema ining subjects, hip impact occurred first, followed by contact of the arm or hand. Published by Elsevier Science Ltd.